MidiService: update listener with current status when registered

This will give an app an opportunity to learn whether an input port is busy
before the user tries to connect and then fails.

Bug: 22825043
Change-Id: Ifede60f166dfe66ea15453044fce06f4a8452b18
Signed-off-by: Phil Burk <philburk@google.com>
(cherry picked from commit b2355940e3)

media/java/android/media/midi/MidiManager.java

@@ -169,6 +169,13 @@ public final class MidiManager {
     /**
      * Registers a callback to receive notifications when MIDI devices are added and removed.
      *
+     * The {@link  DeviceCallback#onDeviceStatusChanged} method will be called immediately
+     * for any devices that have open ports. This allows applications to know which input
+     * ports are already in use and, therefore, unavailable.
+     *
+     * Applications should call {@link #getDevices} before registering the callback
+     * to get a list of devices already added.
+     *
      * @param callback a {@link DeviceCallback} for MIDI device notifications
      * @param handler The {@link android.os.Handler Handler} that will be used for delivering the
      *                device notifications. If handler is null, then the thread used for the

services/midi/java/com/android/server/midi/MidiService.java

@@ -575,6 +575,8 @@ public class MidiService extends IMidiManager.Stub {
         Client client = getClient(token);
         if (client == null) return;
         client.addListener(listener);
+        // Let listener know whether any ports are already busy.
+        updateStickyDeviceStatus(client.mUid, listener);
     }
 
     @Override
@@ -584,6 +586,25 @@ public class MidiService extends IMidiManager.Stub {
         client.removeListener(listener);
     }
 
+    // Inform listener of the status of all known devices.
+    private void updateStickyDeviceStatus(int uid, IMidiDeviceListener listener) {
+        synchronized (mDevicesByInfo) {
+            for (Device device : mDevicesByInfo.values()) {
+                // ignore private devices that our client cannot access
+                if (device.isUidAllowed(uid)) {
+                    try {
+                        MidiDeviceStatus status = device.getDeviceStatus();
+                        if (status != null) {
+                            listener.onDeviceStatusChanged(status);
+                        }
+                    } catch (RemoteException e) {
+                        Log.e(TAG, "remote exception", e);
+                    }
+                }
+            }
+        }
+    }
+
     private static final MidiDeviceInfo[] EMPTY_DEVICE_INFO_ARRAY = new MidiDeviceInfo[0];
 
     public MidiDeviceInfo[] getDevices() {